fs/signalfd.c: fix inconsistent return codes for signalfd4

fs/signalfd.c: fix inconsistent return codes for signalfd4

The kernel signalfd4() syscall returns different error codes when called
either in compat or native mode.  This behaviour makes correct emulation
in qemu and testing programs like LTP more complicated.

Fix the code to always return -in both modes- EFAULT for unaccessible user
memory, and EINVAL when called with an invalid signal mask.

Signed-off-by: Helge Deller <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Laurent Vivier <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>